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125 lines
3.7 KiB
Rust
125 lines
3.7 KiB
Rust
// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
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//! This example shows you how to define ops in Rust and then call them from
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//! JavaScript.
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use anyhow::anyhow;
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use deno_core::json_op_sync;
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use deno_core::JsRuntime;
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use deno_core::Op;
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use serde_json::Value;
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use std::io::Write;
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fn main() {
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// Initialize a runtime instance
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let mut runtime = JsRuntime::new(Default::default());
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// The first thing we do is define two ops. They will be used to show how to
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// pass data to Rust and back to JavaScript.
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//
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// The first one is used to print data to stdout, because by default the
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// JavaScript console functions are just stubs (they don't do anything).
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//
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// The second one just transforms some input and returns it to JavaScript.
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// Register the op for outputting bytes to stdout.
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// It can be invoked with Deno.core.dispatch and the id this method returns
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// or Deno.core.dispatchByName and the name provided.
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runtime.register_op(
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"op_print",
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// The op_fn callback takes a state object OpState
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// and a vector of ZeroCopyBuf's, which are mutable references
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// to ArrayBuffer's in JavaScript.
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|_state, zero_copy| {
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let mut out = std::io::stdout();
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// Write the contents of every buffer to stdout
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for buf in zero_copy {
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out.write_all(&buf).unwrap();
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}
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Op::Sync(Box::new([])) // No meaningful result
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},
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);
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// Register the JSON op for summing a number array.
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// A JSON op is just an op where the first ZeroCopyBuf is a serialized JSON
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// value, the return value is also a serialized JSON value. It can be invoked
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// with Deno.core.jsonOpSync and the name.
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runtime.register_op(
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"op_sum",
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// The json_op_sync function automatically deserializes
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// the first ZeroCopyBuf and serializes the return value
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// to reduce boilerplate
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json_op_sync(|_state, json, zero_copy| {
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// We check that we only got the JSON value,
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// and that it's of the right type.
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if !zero_copy.is_empty() {
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Err(anyhow!("Expected exactly one argument"))
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} else if !json.is_array() {
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Err(anyhow!("Argument is not of type array"))
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} else if !json
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.as_array()
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.unwrap()
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.iter()
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.all(|value| value.is_number())
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{
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Err(anyhow!("Argument is not array of numbers"))
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} else {
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// And if everything checks out we do our actual task
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let sum = json
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.as_array()
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.unwrap()
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.iter()
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.fold(0.0, |a, v| a + v.as_f64().unwrap());
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// Finally we return a JSON value
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Ok(Value::from(sum))
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}
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}),
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);
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// Now we see how to invoke the ops we just defined. The runtime automatically
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// contains a Deno.core object with several functions for interacting with it.
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// You can find its definition in core.js.
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runtime.execute(
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"<init>",
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r#"
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// First we initialize the ops cache.
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// This maps op names to their id's.
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Deno.core.ops();
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// Then we define a print function that uses
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// our op_print op to display the stringified argument.
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const _newline = new Uint8Array([10]);
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function print(value) {
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Deno.core.dispatchByName('op_print', Deno.core.encode(value.toString()), _newline);
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}
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// Finally we register the error class used by op_sum
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// so that it throws the correct class.
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Deno.core.registerErrorClass('Error', Error);
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"#,
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).unwrap();
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// Now we can finally use this in an example.
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runtime
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.execute(
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"<usage>",
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r#"
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const arr = [1, 2, 3];
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print("The sum of");
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print(arr);
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print("is");
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print(Deno.core.jsonOpSync('op_sum', arr));
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// And incorrect usage
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try {
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print(Deno.core.jsonOpSync('op_sum', 0));
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} catch(e) {
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print('Exception:');
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print(e);
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}
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"#,
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)
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.unwrap();
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}
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